Foamed slurry and building panel made therefrom

ABSTRACT

A gypsum slurry is described that includes water, a hydraulic component comprising at least 50% calcined gypsum by weight based on the dry weight of the hydraulic component, foam, a defoamer, a polycarboxylate dispersant having olefinic unsaturated mono-carboxylic acid moieties and (poly)oxyalkylene moieties, a first portion of a retarder and a second portion of a retarder. In some embodiments of the invention, the defoamer is combined with the dispersant prior to being added to the gypsum slurry. The defoamer and dispersant can be added as a physical mixture, wherein the defoamer is attached onto the dispersant polymer, or a combination thereof. In some embodiments, a gypsum building panel is made from the gypsum slurry.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Ser. No. 11/449,924entitled “Gypsum Products Utilizing A Two-Repeating Unit Dispersant AndA Method For Making Them”, filed Jun. 9, 2006, which is acontinuation-in-part of U.S. Ser. No. 11/152,418 entitled “GypsumProducts Utilizing A Two-Repeating Unit Dispersant And A Method ForMaking Them”, filed Jun. 14, 2005, now abandoned, both hereinincorporated by reference.

This application is further related to U.S. Ser. No. 11/894,029, filedconcurrently herewith, entitled “A Liquid Admixture Composition” andherein incorporated by reference.

BACKGROUND OF THE INVENTION

This invention relates to a foamed gypsum slurry. More specifically, itrelates to a foamed gypsum slurry that includes a defoamer to produce adistribution of foam bubbles. The gypsum slurry is useful for makingbuilding panels.

Gypsum building panels offer a high performance product for a reasonableprice for finishing of building spaces. Gypsum, also known as calciumsulfate dihydrate, is heated to drive off crystalline water to producecalcium sulfate anhydrite and/or calcium sulfate hemihydrate, also knownas stucco, calcined gypsum or Plaster of Paris. The building panels aremade by combining dry stucco with water. Calcined gypsum and water arecombined and an interlocking matrix of gypsum crystals is formed. Afterthe hydration of the calcined gypsum, excess water is driven off byheating, the resulting product is a relatively strong panel, having agood surface for receiving decorative finishes such as paint orwallpaper.

Although gypsum building panels are cost effective, they are relativelyheavy. The panels must be moved in small batches due to the weight.Installers who work with the panels become fatigued from lifting thepanels and holding them in place to be secured. Additionally, heavypanels are costly to transport. One method of controlling the density ofthe product is by the addition of a soap-based foam to the liquidslurry. The stucco then sets around the foam bubbles, creating voids inthe gypsum matrix. It is important to control the size of the bubbles toavoid undesirable properties in the panels. If the bubbles are toosmall, a large number of small bubbles are needed to effect the changein density. Where there are lots of bubbles in a confined space, theresulting gypsum matrix has a low compressive strength. Bubbles that aretoo large cause a decrease in strength and form unsightly blisters underthe facing paper.

It has been found that if the gypsum is formed having a mixture of voidsizes, it is possible to produce a building panel that is both strongand free of surface defects. Various soaps produce bubbles havingdifferent properties. Some soaps form bubbles that are very strong andstable, with little tendency to break and coalesce. For the purposes ofthis invention, a stable soap is defined as one developed to maximizeair entrainment and minimize usage in gypsum slurries. Other soaps areless stable, forming foam, but becoming more unstable in the presence ofgypsum. A combination of soaps that form stable and unstable foamsallows for control of the production of larger foam voids in the gypsumslurry. Some embodiments of this invention utilize the combination ofsoaps described in U.S. Pat. No. 5,643,510, herein incorporated byreference.

Reduction in the amount of water needed to produce gypsum is alsodesirable. Water in excess of that needed to hydrate the calcined gypsumis removed by kiln drying. Fuel costs to operate the drying kiln make itadvantageous to reduce the amount of water in a gypsum slurry, whilemaintaining similar flow characteristics.

In an attempt to reduce water usage by use of a polycarboxylatedispersant, it was found that the polycarboxylate dispersant interferedwith formation of the desired bubble size distribution, and the abilityto control formation of larger voids. Panel strength suffered due to theformation of very stable, very small bubbles. Addition of conventionalpolycarboxylate dispersants apparently change the surface chemistry ofthe bubbles, making it more difficult to obtain a desirable corestructure. A desirable core structure is one that is engineered to havea distribution of bubbles in the slurry or voids in the set gypsum thatinclude a number of large voids.

SUMMARY OF THE INVENTION

At least one of these problems is eliminated or reduced by the slurryand method described herein. More specifically, the invention providesfor an improved gypsum slurry that includes water, a hydraulic componentcomprising at least 50% calcined gypsum by weight based on the dryweight of the hydraulic component, foam, a defoamer and apolycarboxylate dispersant. The dispersant is made up of a first and asecond repeating unit, wherein said first repeating unit is an olefinicunsaturated mono-carboxylic acid repeating unit or an ester or saltthereof, or an olefinic unsaturated sulphuric acid repeating unit or asalt thereof, and said second repeating unit is of the general formula(I)

where R¹ is represented by

and wherein R² is hydrogen or an aliphatic C₁ to C₅ hydrocarbon group,R³ is a non-substituted or substituted aryl group and preferably phenyl,and R⁴ is hydrogen or an aliphatic C₁ to C₂₀ hydrocarbon group, acycloaliphatic C₅ to C₈ hydrocarbon group, a substituted C₆ to C₁₄ arylgroup or a group conforming to the formula

wherein R⁵ and R⁷, independently of each other, represent an alkyl,aryl, aralkyl or alkylaryl group and R⁶ is a divalent alkyl, aryl,aralkyl or alkaryl group, p is 0, 1, 2, 3, inclusive, m and n are,independently, an integer from 2, 3, 4, 5, inclusive; x and y are,independently, integers from 1 to 350, inclusive and z is from 0 to 200,inclusive.

A method of reducing water in a gypsum slurry includes preparing agypsum slurry that includes water, calcined gypsum, a defoamer and thedispersant described above. A first portion of retarder is added to theslurry, the first portion being an amount of retarder sufficient tosubstantially prevent buildup of gypsum crystals within the mixer. Asecond portion of retarder is also added to the slurry, the secondportion being an amount of retarder sufficient to increase the fluidityof the slurry beyond that obtained by addition of the first portion ofretarder.

Addition of both portions of retarder not only keeps the mixer free ofgypsum solids, but increases the flowability of the slurry. Since it isdesirable to maintain a constant slurry fluidity, the increasedflowability can be realized as a reduction in water at the samedispersant level, or reduction of dispersant using the same amount ofwater. Either results in a reduction of raw materials and possible costsavings.

Some embodiments include mixtures or combinations of the defoamer andthe dispersant that are combined prior to their addition to the slurry.The defoamer and the slurry are combined in a physical mixture in atleast one embodiment of the invention. In at least one other embodiment,the defoamer is attached onto the dispersant's polymer structure.Combinations of the physical mixture and the attached defoamer are alsouseful.

There is, further, an improvement in fluidity when defoamer is addedwith dispersant to the foamed slurry. This increased flowability resultsin the ability to reduce the amount of water added to the slurry for agiven flowability, or the ability to reduce the amount of dispersant. Ineither case, a possible cost reduction is obtained either from reduceddrying fuel use or a direct reduction in the dispersant use.

DETAILED DESCRIPTION OF THE DRAWING

FIG. 1 is a graph of the void volume as a function of the void diameterfor two different dispersants.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of the present invention is directed to a gypsum slurry.The slurry includes water, a hydraulic component, foam, a defoamer and apolycarboxylate dispersant. Unless otherwise noted, components of theslurry are measured by weight, based on the total dry hydrauliccomponent weight.

The hydraulic component includes at least 50% calcined gypsum by weightbased on the dry weight of the hydraulic component. Preferably, theamount of calcined gypsum in the hydraulic component is greater than50%. Other embodiments of the invention utilize hydraulic componentsthat include greater than 65% or greater than 80% calcined gypsum basedon the dry weight of the hydraulic component. In many wallboardformulations, the hydraulic material is substantially all calcinedgypsum. Any form of calcined gypsum may be used, including but notlimited to alpha or beta stucco. Use of calcium sulfate anhydrite,synthetic gypsum or landplaster is also contemplated. Other hydraulicmaterials, including cement and fly ash, are optionally included in theslurry.

Foam is added to the slurry to control the density of the finishedproduct. Any of the conventional foaming agents known to be useful inpreparing foamed gypsum products can be employed. Many such foamingagents are well known and readily available commercially, e.g. theHYONIC line of soap products from GEO Specialty Chemicals, Ambler, Pa.Foams and one method for preparing foamed gypsum products are disclosedin U.S. Pat. No. 5,683,635, herein incorporated by reference. Thispatent teaches the inclusion of large bubbles into the foam sizedistribution by varying the ratio of a first foaming agent and a secondfoaming agent. Control of foam bubble size is important to the strengthof the finished panel product. The first foaming agent is from about 65%to about 85 wt. % based on the total weight of all foaming agents.

An example of the first foaming agent, useful to generate unstablefoams, has the formula:CH₃(CH₂)_(x)(CH₂)(OCH₂)_(y)OSO₃-M  (VI)

wherein X is a number from 2 to 20, Y is a number from 0 to 10 and isgreater than 0 in at least 50 weight percent of the foaming agent, and Mis a cation.

An example of the second foaming agent, useful to generate stable foams,has the formula:R′—OSO₃-M  (VII)

wherein R′ is an alkyl group containing from 2 to 20 carbon atoms, and Mis a cation. Preferably, R′ is an alkyl group containing from 8 to 12carbon atoms. The cation of either the first or second foaming agent,independently, includes at least one of sodium, potassium, magnesium,ammonium, quaternary ammonium and mixtures thereof.

The addition of one or more defoamers with the polycarboxylatedispersant has been found to permit further altering of the size ofbubbles and thereby control the production of larger voids. As thestucco sets, the interlocking matrix of calcium sulfate dihydratecrystals forms around the bubbles, leaving voids in the set material. Inthe discussion that follows, the exemplary void size distribution isdiscussed as it applies to a gypsum panel core, however, it iscontemplated that the slurry of this invention could be useful in othergypsum-based products.

FIG. 1 is an example of how the change in dispersants can alter thedistribution of the void sizes. When some polycarboxylate dispersantsare used, a large number of tiny, stable bubbles are formed in theslurry. This is seen in the graph of the void size distribution of agypsum product made with MELFLUX PCE 356 L/35% ND, shown on the graph as“356”. Inclusion of a defoamer and optional surfactant in the gypsumproduct labeled “410” (made with MELFLUX PCE 410 L/35% FF) reduces thenumber of tiny voids, and provides a wider distribution of voiddiameters and an increased number of large voids. Gypsum products ofsimilar density having a wide distribution of void diameters arestronger than those having a large number of small voids.

Some embodiments of the invention use a blend of stable and unstablesoaps. In at least one embodiment, the stable soap is a conventionalsoap having an alkyl chain length of 8-12 carbon atoms and an ethoxygroup chain length of 1-4 units. An example of an unstable soap is anunethoxylated soap with an alkyl chain length of 6-16 carbon units. Someembodiments utilize a predominant amount of the stable soap.

When foam is added to the product, the polycarboxylate dispersant isoptionally divided between the gauging water and the foam water or twodifferent dispersants are used in the gauging water and the foam waterprior to its addition to the calcium sulfate hemihydrate. This method isdisclosed in co-pending application U.S. Ser. No. 11/152,404, entitled,“Effective Use of Dispersants in Wallboard Containing Foam”, hereinincorporated by reference.

Dispersants that are contemplated are polycarboxylate dispersants. Therange of the dispersant used is about 0.01 wt % to about 1.0 wt %dispersant solids, based on hydraulic component content. In someembodiments, the polycarboxylate dispersant includes a plurality ofether-linked polyoxyalkylene chains. Two examples of usefulpolycarboxylate dispersants are MELFLUX 1641 F (“1641”) dispersants andMELFLUX 2641 F (“2641”) dispersants. Both are available from BASFConstruction Polymers GmbH, Trostberg, Germany. The 1641 dispersant isdescribed in U.S. Pat. No. 5,798,425, herein incorporated by reference.It is a two-monomer copolymer having vinyl ether and olefinicunsaturated carboxylic ester groups. Another suitable class ofpolycarboxylate dispersants is a three-monomer system exemplified by the2641 dispersant. The co-polymer and a method of making it are describedin U.S. Pat. No. 6,777,517, herein incorporated by reference.

Another dispersant used in some embodiments of the slurry includes tworepeating units. The first repeating unit is an olefinic unsaturatedmono-carboxylic acid repeating unit, an ester or salt thereof, or anolefinic unsaturated sulphuric acid repeating unit or a salt thereof.Examples of the first repeating unit are acrylic acid, methacrylic acid,crotonic acid, isocrotonic acid, allyl sulfonic acid and vinyl sulfonicacid. Mono- or divalent salts are suitable in place of the hydrogen ofthe acid group. The hydrogen can also be replaced by hydrocarbon groupto form the ester. Preferred repeating units include acrylic acid ormethacrylic acid.

The second repeating unit satisfies Formula I,

and R¹ is derived from an unsaturated (poly)alkylene glycol ether groupaccording to Formula II.

Referring to Formulas I and II, the alkenyl repeating unit optionallyincludes a C₁ to C₃ alkyl group between the polymer structure and theether linkage. The value of p is an integer from 0, 1, 2, 3, inclusive.Preferably, p is either 0 or 1. R² is either a hydrogen atom or analiphatic C₁ to C₅ hydrocarbon group, which may be linear, branched,saturated or unsaturated. R³ is a non-substituted or substituted arylgroup, preferably phenyl. Examples of preferred repeating units includeacrylic acid and methacrylic acid.

The polyether group of Formula II contains multiple C₂-C₄ alkyl groups,including at least two alkyl groups, connected by oxygen atoms. The mand n are, independently, integers from 2, 3, 4, 5, inclusive,preferably, at least one of m and n is 2. The x and y are,independently, integers from 1 to 350, inclusive. The value of z is from0 to 200, inclusive. R⁴ is hydrogen or an aliphatic C₁ to C₂₀hydrocarbon group, a cycloaliphatic C₅ to C₈ hydrocarbon group, asubstituted C₆ to C₁₄ aryl group or a group conforming at least one ofFormula III(a), III(b) and III(c).

In the above formulas, R⁵ and R⁷, independently of each other, representan alkyl, aryl, aralkyl or alkylaryl group. R⁶ is a bivalent alkyl,aryl, aralkyl or alkylaryl group.

Dispersants of this group are referenced as the “Melflux PCE”dispersants. Polymers in this series known to be useful in wallboardinclude MELFLUX PCE 211 L/35% ND, MELFLUX PCE 239 L/35% ND, MELFLUX PCE267 L/35% ND and MELFLUX PCE 356 L/35% ND. This class of dispersants andhow to make them is further described in U.S. Ser. No. 11/451,625,entitled “Polyether-Containing Copolymer”, filed Jun. 12, 2006 andherein incorporated by reference. Another suitable dispersant is MELFLUXPCE 410 L/35% FF (“410”), that is made according to U.S. Ser. No.11/894,029, filed concurrently herewith, previously incorporated byreference.

The molecular weight of the dispersant is preferably from about 20,000to about 60,000 Daltons. Surprisingly, it has been found that the lowermolecular weight dispersants cause more retardation of set time thandispersants having a molecular weight greater than 60,000 Daltons.However, tests with gypsum indicate that efficacy of the dispersant isreduced at molecular weights above 60,000 Daltons.

Many polymers can be made with the same two repeating units usingdifferent distributions of them. The ratio of the acid-containingrepeating units to the polyether-containing repeating unit is directlyrelated to the charge density. Preferably, the charge density of theco-polymer is in the range of about 300 to about 3000 μequiv. charges/gco-polymer. However, it has also been discovered that the increase incharge density further results in an increase in the retardive effect ofthe dispersant. Dispersants with a low charge density retard the settimes less than a dispersant having a high charge density. Sinceretardation in set times increases with the increase in efficacyobtained with dispersants of high charge density, making a slurry withlow water, good flowability and reasonable set times requires keeping ofthe charge density in a certain range. Preferably, the charge density ofthe co-polymer is in the range of about 600 to about 2000 μequiv.charges/g co-polymer.

This Melflux PCE dispersant is particularly well-suited for use withgypsum. While not wishing to be bound by theory, it is believed that theacid repeating units bind to the hemihydrate crystals while the longpolyether chains of the second repeating unit on the structure performthe dispersing function. Balancing of the length of the polyetherchains, the total molecular weight and the charge density are importantfactors in designing a dispersant for gypsum. Since the Melflux PCE isless retardive than other dispersants, it is less disruptive to themanufacturing process of certain gypsum products. The dispersant is usedin any effective amount. To a large extent, the amount of dispersantselected is dependant on the desired fluidity of the slurry. As theamount of water decreases, more dispersant is required to maintain aconstant slurry fluidity. Preferably, the dispersant is used in amountsof about 0.01% to about 0.5% based on the dry weight of the stucco. Morepreferably, the dispersant is used in amounts of about 0.05% to about0.2% on the same basis. In measuring a liquid dispersant, only thepolymer solids are considered in calculating the dosage of thedispersant, and the water from the dispersant is considered when awater/stucco ratio is calculated. This dispersant allows for the designof a high-speed wallboard manufacturing process where the board is atleast 50% set within ten minutes. Even in the absence of accelerators,at least 50% set is achievable within ten minutes.

Polymerization of the repeating units to make the copolymer dispersantis carried out by any method known by an artisan. Preferredpolymerization techniques are taught in U.S. Patent Publication No.2006/0281886, entitled “Polyether-Containing Copolymer”, filed Jun. 12,2006 and published Dec. 14, 2006, herein incorporated by reference.

One or more defoamers are added to the slurry to reduce the bubblestability and thereby increase the distribution of bubble sizes. Theaddition of one or more defoamers to this polycarboxylate dispersant hasbeen found to produce active bubbles. Active bubbles continuouslycoalesce, maintaining a size distribution of bubbles. As the stuccosets, the interlocking matrix of calcium sulfate dihydrate crystalsforms around the bubbles, leaving voids in the set material. Anydefoaming agent can be added to the slurry, including non-ionicsurfactants such as copolymers comprising ethylene oxide/propyleneoxide-(PO-EO)- units (Dowfax of the Dow Company, Midland, Mich.),EO-PO-EO or PO-EO-PO block polymers, respectively (PLURONIC of BASF) orpolysiloxane dispersions such as siloxane by Wacker Chemie AG.

In some embodiments where it is added separate from the dispersant, thesilicone compound is a polymerizable siloxane in the form of a stableemulsion. In some embodiments, it is added to the slurry at the mixer.The slurry is then shaped and dried under conditions which promote thepolymerization of the siloxane to form a highly cross-linked siliconeresin. Preferably, a catalyst which promotes the polymerization of thesiloxane to form a highly cross-linked silicone resin is also added tothe slurry.

The siloxane is often a fluid, linear hydrogen-modified siloxane, butcan also be a cyclic hydrogen-modified siloxane. Such siloxanes arecapable of forming highly cross-linked silicone resins. These fluids arewell known to an artisan and are commercially available. Typically, thelinear hydrogen-modified siloxanes useful are those of the generalformula:R″HSiO_(2/2)where R″ represents a saturated or unsaturated monovalent hydrocarbonradical. In preferred embodiments, R″ represents an alkyl group and mostpreferably R″ is methyl.

The siloxane emulsion is preferably added to the gauging water beforethe slurry is formed in order to provide sufficient time for thesiloxane emulsion to thoroughly mix with water used to form the slurry.The siloxane emulsion is preferably stabilized prior to addition to thegauging water and well dispersed in the slurry, particularly followingthe addition of optional additives and during subsequent process steps.A stable siloxane/water emulsion is optionally prepared by combining thesiloxane fluid with a small amount of water in a high intensity mixerfor 1-2 seconds. No chemical emulsifier is needed. The emulsion thusformed is sufficiently stable that the silicone fluid mixes with thegauging water and remains dispersed while polymerization occurs.Pre-made siloxane emulsions are also useful.

Some embodiments of the invention utilize a methyl hydrogen polysiloxanefluid sold under the name SILRES BS-94 by Wacker-Chemie GmbH as thesiloxane. Preferably 0.3 to about 1.0 weight % of the BS-94 fluid isused, based on the weight of the dry stucco. At least one embodimentuses the siloxane fluid in amounts of about 0.4 to about 0.8 weight % onthe same basis. Powdered methyl hydrogen polysiloxanes, such as WACKERBS Powder A and WACKER BS Powder G, are also useful.

The hydrogen polysiloxane cures by forming a reactive silanol compound.Polymerization of the siloxane in situ proceeds slowly, taking days orweeks to fully cure. The addition of a catalyst improves the cure rateof the siloxane. Any catalyst, including alkaline earth oxides andhydroxides, known in the prior art is useful. At least some embodimentsutilize a dead-burned or hard-burned magnesium oxide catalyst. Baymag 96(Baymag, Inc., Calgary, Alberta, Calif.) is a commercially availabledead-burned magnesium oxide suitable as a catalyst.

Relatively small amounts of the catalyst are needed. About 0.1 to about0.5% by weight, based on dry calcined gypsum weight, preferably 0.2 toabout 0.4% by weight, is used. Preferably, the catalyst has a loss onignition of less than 0.1% by weight and has a surface area of at least0.3 m²/g. Additional information regarding the use of magnesium oxidecatalysts for curing of siloxane is found in commonly owned U.S. PatentApplication Publication No. 2006/0035112, published Feb. 16, 2006,herein incorporated by reference.

The defoamer is optionally added to the slurry in a number of differentways. In at least one embodiment, the defoamer and dispersant are addedseparately as independent compounds. The weight ratio of the dispersantto the defoamer ranges from about 1000:1 to about 1:1. Addition of thedefoamer to the slurry mixer with the polycarboxylate dispersant iscontemplated; however, addition of the defoamer to the foam water isalso possible.

In yet another embodiment of the invention, the defoamer is combinedwith the dispersant and the optional surfactant in a liquid compositionprior to addition to the gypsum slurry. MELFLUX PCE 410 L/35% FF (BASFConstruction Polymers GmbH) is an example of a dispersant combined witha defoamer, optional surfactant and water that provides improvedstability over time and which allows homogeneous dosing in wallboardproduction. Any surfactant is useful that stabilizes the defoamer in theaqueous mixture. Useful surfactants include an ethylene oxide/propyleneoxide block copolymer, an alcohol ethyloxide R¹³-(EO)—H with R¹³ beingselected from the group consisting of an aliphatic hydrocarbon grouphaving from 1 to 20 carbon atoms, acetylenic diols,monoalkylpolyalkylenes, ethoxylated nonylphenols, alkylethersulfonatesand combinations thereof, a styrene/maleic acid copolymer, a fattyalcohol alkoxylate or an alcohol having a carbon chain length of 2 to 20carbon atoms and a polyalkylene group. Use of combinations of thesesurfactants is also contemplated. The weight ratio of the dispersant tothe surfactant is about 1000:1 to about 1:1.

A further embodiment of the invention is contemplated whereby a firstportion of the defoamer is attached to the dispersant chain, while asecond portion of the defoamer is unattached. This would occur, forexample, where only the first portion of the defoamer was successfullyattached to the dispersant polymer chain. The second portion of defoamercould then be present in the aqueous admixture to provide defoamingaction in addition to that provided by the attached defoamer. If presentin the aqueous admixture, the unattached defoamer would be physicallydispersed in the mixture. If present in the gypsum slurry, theunattached defoamer would be substantially dispersed in the slurry.

When the defoamer is present as a third moiety attached onto thedispersant, the additional monomer should be represented in thecopolymer in amounts up to about 5 mol %, or from about 0.05 to about 3mol %. Examples of the third moiety include structures of the FormulasIV(a) and IV(b):

In the formula IV(a), R⁸ can be H or CH₃ depending on whether thestructural units are acrylic or methacrylic acid derivatives. In formulaIV(b), R⁹ can be hydrogen, an aliphatic hydrocarbon radical having from1 to 20 carbon atoms, a cycloaliphatic hydrocarbon radical having from 5to 8 carbon atoms, an aryl radical having from 6 to 14 carbon atomswhich may also be substituted. S can be —H, —COO_(a)M or —COOR¹¹, wherea is ½ or 1, M is a hydrogen, a monovalent or divalent metal cation, anammonium ion or an organic amine radical, R¹¹ is an aliphatichydrocarbon radical having from 3 to 20 carbon atoms, a cycloaliphatichydrocarbons radical having from 5 to 8 carbon atoms or an aryl radicalhaving from 6 to 14 carbon atoms. The aliphatic hydrocarbon radical canbe linear or branched, saturated or unsaturated. Preferredcycloaliphatic hydrocarbon radicals are cyclopentyl or cyclohexylradicals; preferred aryl radicals are phenyl or naphthyl radicals. Inthe case of T=—COOR⁵, S=COO_(a)M or —COOR⁵. When both T and S are—COOR⁵, the corresponding structural units are derived from dicarboxylicesters. From about 0.1 to 5 mol % of the structural units are thedefoaming moieties.

Apart from these ester groups, the structural units may also includeother hydrophobic structural elements. These include polypropylene oxideor polypropylene oxide-polyethylene oxide derivatives of the formula V:

X is from 1 to 150 and y is from 0 to 15. The polypropyleneoxide(polyethylene oxide) derivatives can be linked via a group U¹ tothe ethyl radical of the structural unit corresponding to the formulaIV(a), where U¹=—CO—NH—, —O—, or —CH₂—O—. The structural unit is thusthe amide, vinyl ether or allyl ether corresponding to the structuralunit of the formula IV(a). R¹⁰ may in turn be as defined for R⁹ (seeabove) or be

where U²=—NH—CO—, —O—, —OCH₂— and S is as defined above. These compoundsare polypropylene oxide (-polyethylene oxide) derivatives of thebifunctional alkenyl compounds corresponding to the formula IV(a).

As a further hydrophobic structural element, the compounds of theformula IV(a) may contain polydimethylsiloxane groups, which formulaIV(a) corresponds to T=—W—R⁷. W is:

(hereinafter referred to as a polydimethylsiloxane group), R⁷ can be asdefined for R² and n can be from 2 to 100.

The polydimethylsiloxane group can not only be bound directly to theethylene radical of the formula IV(a), but also via the group—CO—[NH—(CH₂)_(s)]—W—R¹² or —CO—O(CH₂)—W—R¹², where R¹² is preferably asdefined for R⁹ and s=1 or 2 and z=0 to 2. R¹² may also be a radical ofthe formula:

The compounds are bifunctional ethylene compounds of the formula IV(a)which are linked to one another via the respective amide or estergroups, with only one ethylene group having been copolymerized.

A similar situation applies to the compounds of the formula IV(a) inwhich T=(CH₂)_(z)—V—(CH₂)_(z)—CH═CH—R², where z=0 to 4, V is either apolydimethylsiloxane radical W or a —O—CO—C₆H₄—CO—O— radical and R⁹ isas defined above. These compounds are derived from the correspondingdialkylphenyldicarboxylic acid esters or dialkylenepolydimethylsiloxanederivatives.

Alternatively, other co-monomers, such as styrene or acrylamides areco-polymerized with the primary two monomers. Components withhydrophobic properties may be used. Compounds with ester structuralunits, polypropylene oxide or polypropylene oxide-polyethylene oxide(PO/PE), polybutylene oxide-polyoxyethylene (PB/PE) or polystyreneoxide-polyethylene oxide (PS/PE) units are preferred. Compoundsdisclosed by U.S. Pat. Nos. 5,798,425 and 6,777,517 are also preferred.

The aqueous mixture is then preferably added to the gauging water beforethe mixer, to foam water, or to the mixer as a separate stream. Additionof the solution during other process steps is also contemplated.

Water is added to the slurry in any amount that makes a flowable slurry.The amount of water to be used varies greatly according to theapplication with which it is being used, the exact dispersant beingused, the properties of the stucco and the additives being used. Thewater to stucco ratio (“WSR”) with wallboard is preferably about 0.1 toabout 0.9 based on the dry weight of the stucco. Commonly a WSR of about0.2 to about 0.85 is preferred. Flooring compositions preferably use aWSR from about 0.17 to about 0.45, preferably from about 0.17 to about0.34. Moldable or castable products preferably use water in a WSR offrom about 0.1 to about 0.3, preferably from about 0.16 to about 0.25.The WSR can be reduced to 0.1 or less in laboratory tests based on themoderate addition of the Melflux PCE dispersants.

Water used to make the slurry should be as pure as practical for bestcontrol of the properties of both the slurry and the set plaster. Saltsand organic compounds are well known to modify the set time of theslurry, varying widely from accelerators to set inhibitors. Someimpurities lead to irregularities in the structure as the interlockingmatrix of dihydrate crystals forms, reducing the strength of the setproduct. Product strength and consistency is thus enhanced by the use ofwater that is as contaminant-free as practical.

Surprisingly, it has also been found that the use of some retarders withthe Melflux PCE family of dispersants gives an unexpected increase inthe dispersant efficacy. Normally a first portion of retarder is addedto the slurry to prevent solids build-up in the mixer and associatedslurry contacting parts. If the calcined gypsum starts to set, dihydratecrystals deposit on the mixer interior and associated slurry contactingparts. Some retarders delay the onset of crystallization, therebypreventing set gypsum lumps from forming while the slurry is inside themixer and associated slurry contacting parts, which could later breakfree to negatively impact the product and/or production thereof. Thefirst portion of set retarders is normally added in amounts of up toabout 1 lb./MSF (4.9 g/m²). The exact amount of retarder used for aparticular slurry varies greatly depending on the properties of thegypsum and other raw materials used, type of calcination, amount andtypes of additives present.

However, in the presence of Melflux PCE dispersants, a second portion ofthe retarder appears to have the ability to reduce the amount of water,dispersant or both needed to fluidize the slurry even beyond thatnecessary to keep the mixer clean and substantially free of gypsumsolids. Further, the reduction in PCE dosage changes non-linearly as theamount of retarder is added linearly. For example, the synergistic useof VERSENEX 80E Chelating Agent (Dow Chemical Co., Midland, Mich.) withMelflux 410 L/35% FF dispersant has been shown to allow reduction in theamount of dispersant up to 37%, based on making a slurry of constantfluidity and similar set characteristics. In some embodiments of thepresent invention, the second portion of retarder is about 0.05 to about0.3 lb/MSF in addition to the first portion of retarder. In otherembodiments, ranges for the second retarder are about 0.05 to about 0.5lb/MSF or about 0.5 to about 1 lb/MSF. Larger second portion doses canbe used where any developing processing issues can be overcome. If theproduct is too soft at the knife for cutting, a certain amount ofaccelerator can be added to overcome the effects of the retarder.

The first retarder portion and the second retarder portion can be addedto the slurry either individually or as a combined dose. The retarder isuseful as either the first portion of the retarder, the second portionof the retarder or both. Some embodiments of the invention utilize adiethylenetriaminepenta-acetate (DTPA) retarder. At least one embodimentuses pentasodium DTPA, known as VERSENEX 80E. Other retarders areexpected to show similar improvement in PCE efficacy, including pentasodium salt of amino tri(methylene phosphonic acid) (Dequest 2006dispersant, Thermphos Trading GmbH), tartaric acid, succinic acid,citric acid, maleic acid and their corresponding salts (Na, K, NH₄, Li).

Additional additives are also added to the slurry as are typical for theparticular application to which the gypsum slurry will be put. Dryaccelerators (up to about 45 lb./MSF (219 g/m²)) are added to modify therate at which the hydration reactions take place. “CSA” is a setaccelerator comprising 95% calcium sulfate dihydrate co-ground with 5%sugar and heated to 250° F. (121° C.) to caramelize the sugar. CSA isavailable from United States Gypsum Company, Southard, Okla. plant, andis made according to U.S. Pat. No. 3,573,947, herein incorporated byreference. Potassium sulfate, aluminum sulfate, sodium sulfate andsodium bisulfate are other preferred accelerators. HRA is calciumsulfate dihydrate freshly ground with sugar at a ratio of about 3 to 25pounds of sugar per 100 pounds of calcium sulfate dihydrate. It isfurther described in U.S. Pat. No. 2,078,199, herein incorporated byreference. Starch may be used in place of the sugar as taught in U.S.Pat. No. 4,019,920, herein incorporated by reference. Other acceleratorsmay be used as are known to those skilled in the art.

Another accelerator, known as wet gypsum accelerator or WGA, is also apreferred accelerator. A description of the use of and a method formaking wet gypsum accelerator are disclosed in U.S. Pat. No. 6,409,825,herein incorporated by reference. This accelerator includes at least oneadditive selected from the group consisting of an organic phosphoniccompound, a phosphate-containing compound or mixtures thereof. The wetgypsum accelerator is used in amounts ranging from about 5 to about 80pounds per thousand square feet (24.3 to 390 g/m²) of board product.

In some embodiments of the invention, additives are included in thegypsum slurry to modify one or more properties of the final product.Additives are used in the manner and amounts as are known in the art.Concentrations are reported in amounts per 1000 square feet of finishedboard panels (“MSF”). Glass fibers or paper fibers are optionally addedto the slurry. Wax emulsions or silioxanes are added to the gypsumslurry to improve the water-resistency of the finished gypsum boardpanel.

A trimetaphosphate compound is added to the gypsum slurry in someembodiments to enhance the strength of the product and to improve sagresistance of the set gypsum. Preferably the concentration of thetrimetaphosphate compound is from about 0.004% to about 2.0% based onthe weight of the calcined gypsum. Gypsum compositions includingtrimetaphosphate compounds are disclosed in U.S. Pat. Nos. 6,342,284 and6,632,550, both herein incorporated by reference. Exemplarytrimetaphosphate salts include sodium, potassium or lithium salts oftrimetaphosphate, such as those available from Astaris, LLC., St. Louis,Mo. Care must be exercised when using trimetaphosphate with lime orother modifiers that raise the pH of the slurry. Above a pH of about9.5, the trimetaphosphate loses its ability to strengthen the productand the slurry becomes severely retardive.

Other potential additives to the wallboard are biocides to reduce growthof mold, mildew or fungi. Depending on the biocide selected and theintended use for the wallboard, the biocide can be added to thecovering, the gypsum core or both. Examples of biocides include boricacid, pyrithione salts and copper salts. Biocides can be added to eitherthe covering or the gypsum core. When used, biocides are used in thecoverings in amounts of less than 500 ppm.

In addition, the gypsum composition optionally can include a starch,such as a pregelatinized starch or an acid-modified starch. Theinclusion of the pregelatinized starch increases the strength of the setand dried gypsum cast and minimizes or avoids the risk of paperdelamination. One of ordinary skill in the art will appreciate methodsof pregelatinizing raw starch, such as, for example, cooking raw starchin water at temperatures of at least about 185° F. (85° C.) or othermethods. Suitable examples of pregelatinized starch include, but are notlimited to, PCF 1000 starch, commercially available from Bunge MillingInc (St. Louis, Mo.) and AMERIKOR 818 and HQM PREGEL starches, bothcommercially available from Archer Daniels Midland Company. If included,the pregelatinized starch is present in any suitable amount. Forexample, if included, the pregelatinized starch in either dry powder orliquid form can be added to the mixture used to form the set gypsumcomposition such that it is present in an amount of from about 0.5% toabout 1.5% percent solids by weight of stucco.

Other known additives may be used as needed to modify specificproperties of the product. Sugars, such as dextrose, are used to improvethe paper bond at the ends of the boards. If stiffness is needed, boricacid is commonly added. Fire retardancy can be improved by the additionof vermiculite. These and other known additives are useful in thepresent slurry and wallboard formulations.

In operation, the calcined gypsum is moved in a conveyor toward a mixer.Prior to entry into the mixer, dry additives, such as dry setaccelerators, are added to the powdered calcined gypsum. Other additivesmay also be added to the water. This is particularly convenient wherethe additives are in liquid form. For most additives, there is nocriticality regarding placing the additives in the slurry, and they maybe added using whatever equipment or method is convenient. When usingthe Melflux PCE dispersant, it is important to add the dispersant to thewater prior to addition of the stucco.

The foamed slurry travels to the board line in a soft, pliable bootwhere it is deposited on a paper facing sheet and spread across thewidth of the sheet. A second paper facing sheet is optionally applied tothe top of the slurry, forming a sandwich of continuous gypsum board.The sandwich then passed under a forming plate to press the facing intothe soft slurry and to level the forming board to a consistentthickness.

In some embodiments, the gypsum product is made by an iterative processfor “fine tuning” the void size distribution. The optimum void sizedistribution for a particular product is, in some cases, partiallydefined by local markets. Variations in raw materials or other processconditions can also have an effect on the void size distribution. Toobtain a desirable void size distribution, or to maintain a distributionunder varying conditions, it may be advantageous to make changes orcorrections in the void size distribution. In some embodiments, the voidsize distribution can be varied even after the amount and type ofpolycarboxylate dispersant and defoamer have been fixed. Whileadjustments are being made using this method, it is assumed that otherprocess conditions, particularly the water to stucco ratio, are beingheld substantially constant.

In this method, changes are made to the initial concentration of theaqueous soap mixture of the one or more soaps and the foam water. Usefulranges for the weight concentration of soap in the aqueous soap mixturefor various embodiments are from about 0.1% to about 2%, about 0.1 toabout 1.5%, from about 0.2% to about 1% from about 0.15% to about 0.75%from about 0.3% to about 0.75%, from about 0.25 to about 0.5% from about0.2% to about 0.4% and from about 1% to about 2%.

The foam is pregenerated from the aqueous soap mixture. One method ofmaking the foam is using a foam generator that mixes the soap solutionwith air. Any method of mixing can be used to combine the soap with airthat causes bubbles to be formed, including agitation, turbulent flow ormixing. The amount of water and air are controlled to generate foam of aparticular density. Adjustment of the foam volume is used to control theoverall dry product weight.

Such a foaming agent mixture can be pre-blended “off-line”, i.e.,separate from the process of preparing the foamed gypsum product.However, it is preferable to blend the first and second foaming agentsconcurrently and continuously, as an integral “on-line” part of themixing process. This can be accomplished, for example, by pumpingseparate streams of the different foaming agents and bringing thestreams together at, or just prior to, a foam generator that is employedto generate the stream of aqueous foam which is then inserted into andmixed with the calcined gypsum slurry. By blending in this manner, theratio of the first and second foaming agents in the blend can be simplyand efficiently adjusted (for example, by changing the flow rate of oneor both of the separate streams) to achieve the desired voidcharacteristics in the foamed set gypsum product. Such adjustment willbe made in response to an examination of the final product to determinewhether such adjustment is needed. Further description of such “on-line”blending and adjusting can be found in U.S. Pat. Nos. 5,643,510 and5,683,635, previously incorporated by reference.

The gypsum slurry is prepared by combining gauging water, the hydrauliccomponent, the defoamer and the polycarboxylate dispersant and mixingthem until a homogeneous slurry is obtained. The dispersant ispreferably added to the gauging water, the foam water, split between thegauging and foam water or added directly to the mixer. Dry componentsare combined at the stucco conveyor and moved by conveyor to the mixer.As the conveyor moves, optional dry components including clay and setaccelerators may be added to the stucco. The dry components and gaugingwater were continuously added to a high-shear mixer to form the gypsumslurry. Optional wet components, such as anti-sag agents and setretarders, are added directly to the mixer. The amount of gauging water,dispersant or both are varied to maintain a constant slump patty size,described in more detail below.

The slurry and the pregenerated foam are combined to make a foamedgypsum core. One method of combining the gypsum slurry and thepregenerated foam is by pressurizing the foam and forcing it into theslurry. At least one embodiment uses a foam ring to distribute the foam.The foam ring is a shaped apparatus that allows the slurry to flowthrough it. It includes one or more jets or slots for discharge of thepressurized foam into the slurry as the slurry passes the ring. Use of afoam ring is disclosed in U.S. Pat. No. 5,683,635, herein incorporatedby reference. Another method of combining the foam and the slurry is byaddition of the foam directly to the mixer.

Void size distribution of the foamed gypsum core can be finelycontrolled by adjusting the concentration of the soaps in the aqueoussoap mixture. After a foamed gypsum core has been prepared, inspectionof the interior of the gypsum core reveals the void structure. Changesin the void size distribution are produced by varying the soapconcentration from the initial or previous concentration. If theinterior has too large a fraction of small voids, the soap concentrationin the aqueous soap mixture is reduced. If too many very large, oblongor irregularly shaped voids are found, the soap concentration should beincreased. Although the optimum void size distribution may vary byproduct, location or raw materials used, this process technique isuseful to move towards the desired void size distribution, regardless ofhow it is defined. The desirable void size distribution in manyembodiments is one that produces a high strength core for the gypsumformulation being used.

For example, in some embodiments, the foamed gypsum core should have avoid size distribution where the cumulative volume of voids smaller than0.25 mm is less than the cumulative volume of voids greater than 0.25mm. Substantially all of the total volume of voids should substantiallybe of voids less than or equal to about 1.4 mm in diameter. When thesecriteria are not met, the concentration of soap in the aqueous soapmixture is adjusted and further samples examined. The concentration ofsoap in the aqueous soap mixture should be reduced if the cumulativevolume of voids smaller than about 0.25 mm is too large. If asignificant fraction of the total volume of voids is in voids having adiameter more than 1.4 mm, the concentration of soap in the aqueous soapmixture should be increased. The criteria named above are but twoaspects of the optimum core structure of some particular embodiments.

This process is repeatable as often as needed to produce or maintain adesired void size distribution. It is also useful in combination withother methods of changing the void size distribution, such as varyingthe type or amount of dispersant, varying the foam density or the ratioof stable to unstable soaps, to achieve greater control over the voidsize distribution.

EXAMPLE 1

A plant trial was conducted to compare naphthalene sulfonate condensatedispersants (“NS”) with polycarboxylate dispersants. During the trial, aconstant line speed of 215 ft/min of gypsum building panel was produced.The components used in each sample and the process conditions are shownin Table 1 below. Unless otherwise noted, the amount of each of theremaining components is listed in pounds per 1000 square feet ofbuilding panel product. “WSR” is the water to stucco ratio, where bothfoam water, additive water and gauging water are included. Glass fiberswere added to all samples at the rate of 0.32% based on the stuccoweight. Dextrose was added at 0.17% based on the stucco weight. Thesetwo components were added to each of the samples.

Two polycarboxylate dispersants were used. MELFLUX PCE 356 L/35% ND(“356”) was a dispersant in water without defoamer and without theoptional surfactant. MELFLUX PCE 410 L/35% FF was an aqueous mixture ofa polycarboxylate dispersant, a defoamer, a surfactant and water.

The NS dispersant used was Diloflo-CA (Geo Specialty Chemicals,Lafayette, Ind.). In preparation of the foam, Polystep B25 and SteolCS230 soaps (Stepan Company, Northfield, Ill.) were used.

During preparation of the slurry, the amount of dispersant used wasvaried to create a slurry of substantially uniform flowability asmeasured by a slump test. The amount of HRA was then adjusted to theminimum amount that gave good hardness at the cutting knife.

TABLE 1 Description A B C D Stucco 1778 1778 1778 1778 Gauging Water1093 1084 1081 1079 Foam Water 65 66 65 66 Total Water 1182 1179 11791178 % WSR 66.5% 66.3% 66.3% 66.3% Dispersant NS 410 NS 356 Dispersant12 6 12 9 Amount HRA 18 27 21 33 Retarder 0.38 0.28 0.42 0.20 Starch 5 55 5 Clay 34 34 34 34 Total Soap 0.315 0.315 0.355 0.299 % Unstable 40%35% 40% 40% Soap

Dry components, including the stucco, HRA, starch and clay, werecombined prior to continuous addition to the mixer. The gauging waterand dispersant were continuously added to the mixer. Meanwhile, thesoaps were combined with the foam water to generate a foam external tothe mixer. As the slurry was continuously discharged from the mixer, thefoam was forced, under pressure, into the slurry. Turbulence as theslurry moved down a soft hose to the forming table was sufficient toblend the foam and the slurry together.

At the forming table, the slurry was deposited onto a facing paper. Asecond sheet of facing paper was placed on top of the slurry to form aboard “sandwich”. The sandwich was then passed under a forming plate toevenly distribute the slurry across the width of the paper and to createa sandwich of uniform thickness. The continuous sandwich was then cutinto panels at the knife and kiln dried.

As can be seen from Table 1, less dispersant was used in samplescontaining polycarboxylate dispersants compared to NS dispersants.Further, the 410 dispersant that included the defoamer and surfactantcould be used in lower doses than the polycarboxylate dispersant alone.The amounts of retarder and soap were sometimes reduced with thepolycarboxylate dispersants, as part of the iterative manufacturingprocess. Reduction in the amount of dispersant results in a possiblecost savings therefrom.

EXAMPLE 2

About 600 grams of calcined gypsum from a western gypsum source was usedto make a slurry having a water stucco ratio (WSR) of 0.64. Melflux PCE410 L/35% FF was added in amounts to provide constant patty size from aslump test.

Foam was generated in a separate foam generator and added to the mixerduring the last part of the mixing time. The foam was prepared with afoam generator from a mixture of soap and foam water that included about0.75% soap. The soap was a 90:10 blend of HYONIC PFM-33 (GEO SpecialtyChemicals, Ambler, Pa.) and Steol CS-330. (Stepan Co., Northfield,Ill.). The following procedure describes the remaining processconditions.

The mixing sequence and procedure follows:

1. Water, dispersant, and additives were placed in the Hobart mixer bowland then mixed by hand.

2. Stucco pre-blended with accelerator and specific additives were addedto the bowl and soaked for a short time before the mechanical mixingbegins.

3. During mixing, foam was added for density control. The amount of foamaddition was varied depending on the targeted density.

4. The slurry was mixed for an additional time after the foam additionended.

5. The slurry was then tested for slump, stiffening time, density andcore structure.

To assure that the tests truly reflected the ability to reducedispersant dose, it was necessary to adjust other parameters as theamount of retarder was varied. The water/stucco ratio, slump, stiffeningtime and dry density were kept constant. The slump test is described inU.S. Patent Application Publication No. 2006-0281837, published Dec. 14,2006, herein incorporated by reference.

All tests were run with the same amount of water to ensure that thewater/stucco ratio was the same. If the amount of foam was changed, thegauging water was adjusted so that the total water remained constant.After the amount of retarder was changed, the amount of dispersant wasadjusted to maintain a target slump of 18±0.5 cm.

Increase in the retarder sometimes resulted in a lengthening of thestiffening time, and in such cases the amount of accelerator wasadjusted to maintain a constant stiffening time of 100±5 seconds. In theTable 2 that follows, “amount” refers to the amount of retarder inlbs/MSF, “stiff” refers to stiffening time in seconds and “CSA” refersto the amount of CSA accelerator in grams.

PCE refers to the amount of MELFLUX PCE 410 L/35% FF dispersant presentin grams, while “dose” is the dry-basis amount of dispersant as a weightpercent of the dry calcined gypsum weight. Change in the amount ofdispersant can change the foaming characteristics of the slurry,therefore the amount of foam was varied to maintain a target dry densityof the gypsum cast of 37±1 lb/ft³. The mold for this cast was a 207 mlcup measuring 9.1 cm in height, and filled to the brim. If the slurrysettled more than 2 mm from the rim of the cup while the cast wassetting, the foam was not sufficiently stable and the test was repeatedwith a higher concentration of stable soap. Inspection of the interiorof the gypsum cast revealed the bubble structure. If all samples hadsmall bubbles, the test was repeated with a lower soap concentration. Ifvery large, oblong or irregularly shaped bubbles were found, the testwas repeated with a higher soap concentration. When the adjustments insoaps, dispersant and accelerator were made so that the casts weresubstantially similar, the % PCE Reduction was calculated as thedifference in the amount of PCE used as a percentage of the amount ofPCE used in the control sample.

TABLE 2 Run CSA, PCE, Dose, Retarder, Slump, Stiff, % PCE # g g %lbs/MSF cm sec Reduction 1 2.6 2.57 0.150 0.05 18.0 100 Control 2 2.92.40 0.140 0.10 18.0 100 6.6 3 3.2 2.10 0.123 0.15 17.5 100 18.3 4 4.01.60 0.093 0.25 18.0 105 37.7

The % PCE reduction shown in these runs is non-linear and is indicativeof a synergistic effect between this retarder and the dispersant with adefoaming moiety attached.

EXAMPLE 3

About 600 grams of calcined gypsum from a western gypsum source was usedto make a slurry having a water stucco ratio (WSR) of 0.730. This WSRwas selected in order to achieve a slump patty size of 18±0.5 cm withoutany dispersant or retarder.

Foam was generated in a separate foam generator and added to the mixerduring the last part of the mixing time. The foam was prepared with afoam generator from a mixture of soap and foam water that included about0.75% soap. The soap was added with various blends of HYONIC PFM-33 (GeoSpecialty Chemicals, Lafayette, Ind.) and Steol CS-330 (Stepan Co.,Northfield, Ill.) to produce a similar core void distribution in allcases. The following procedure describes the remaining processconditions.

The mixing sequence and procedure follows:

1. Water, any dispersant, and additives were placed in the Hobart mixerbowl and then mixed by hand.

2. Stucco pre-blended with accelerator and specific additives were addedto the bowl and soaked for a short time before the mechanical mixingbegins.

3. During mixing, foam was added for density control. The amount of foamaddition varied depending on the targeted density.

4. The slurry was mixed for an additional time after the foam additionends.

5. The slurry was then tested for slump, stiffening time, density, andcore structure.

This set of tests included four conditions, for slurries with andwithout retarder, and with and without dispersant. For each condition,the following parameters were held substantially constant: stiffeningtime, dry density target, slump patty size, and core void distribution.The slump test was described in U.S. Patent Application Publication No.2006-0281837, published Dec. 14, 2006, previously incorporated byreference.

If the amount of foam was changed to achieve the desired density, thegauging water was adjusted to balance the change in foam water. Theamount of dispersant remained constant in Run #3 and Run #4 whencomparing slurries made with and without retarder. Similarly, the amountof retarder remained constant in Run #2 and Run #4 when comparingslurries made with and without dispersant.

Amount of accelerator was adjusted to achieve the desired stiffeningtime of 115±5 seconds, and the WSR was adjusted to maintain a targetslump of 18±0.5 cm throughout the study.

Change in the amount of dispersant or WSR can change the foamingcharacteristics of the slurry, therefore the amount of foam was variedto achieve the dry density target of 41±1 lbs/ft³. A portion of theslurry was used to fill a 207 ml cup measuring 9.1 cm in height. If theslurry settled more than 2 mm from the rim of the cup while the cast wassetting, the foam was not sufficiently stable and the test was repeatedwith a higher concentration of stable soap. Inspection of the interiorof the gypsum cast revealed the bubble structure. If all samples hadsmall bubbles, the test was repeated with a lower soap concentration. Ifvery large, oblong or irregularly shaped bubbles were found, the testwas repeated with a higher soap concentration. Adjustments in soaps,accelerator and water were made until the products of each conditionwere substantially similar. The “WSR Reduction” was calculated bycomparing the difference of WSR for each condition versus the controlsample from Run #1.

In Table 3 that follows, “Retarder” refers to the amount of retarder inlbs/MSF, “stiff” refers to stiffening time in seconds and “CSA” refersto the amount of CSA accelerator in grams.

“Dispersant” indicates the type of dispersant, while “Dispersant (g)”indicates the amount of dispersant, on a wet basis at 35% solids. “Dose”is the dry-basis amount of dispersant expressed in percent of the drycalcined gypsum weight.

The WSR Reduction of Run #4 with PCE-410 dispersant and retarder was0.095. This is greater than the sum of the individual effects of Run #2(the impact of retarder alone which is 0.010 WSR Reduction) and Run #3(the impact of PCE alone which is 0.075 WSR Reduction). Thisdemonstrates a synergistic effect between this retarder and dispersantwith a defoaming moiety attached thereto.

While particular embodiments of the foamed slurry and building panelmade therefrom have been shown and described, it will be appreciated bythose skilled in the art that changes and modifications may be madethereto without departing from the invention in its broader aspects andas set forth in the following claims.

TABLE 3 WSR Run CSA Dose Dispersant Reduction Retarder Slump Stiff # WSR(g) Dispersant (%) (g) vs Run#1 (lb/MSF) (cm) (sec) 1 0.730 1.0 None0.000 0.00 0 17.8 120 2 0.720 1.4 None 0.000 0.00 0.010 0.15 17.5 120 30.655 2.0 PCE-410 0.106 1.81 0.075 0 17.5 110 4 0.635 2.6 PCE-410 0.1061.81 0.095 0.15 17.8 115

1. A method of reducing water in a gypsum slurry, comprising: preparinga gypsum slurry comprising water, calcined gypsum, a defoamer and adispersant, wherein the dispersant consists essentially of a first and asecond repeating unit, wherein said first repeating unit is an olefinicunsaturated mono-carboxylic acid repeating unit or an ester or saltthereof, or an olefinic unsaturated sulphuric acid repeating unit or asalt thereof, and said second repeating unit is of the general formula(I)

where R¹ is represented by

and wherein R² is hydrogen or an aliphatic C₁ to C₅ hydrocarbon group,R³ is a non-substituted or substituted aryl group, and R⁴ is hydrogen oran aliphatic C₁ to C₂₀ hydrocarbon group, a cycloaliphatic C₅ to C₈hydrocarbon group, a substituted C₆ to C₁₄ aryl group or a groupconforming to the formula

wherein R⁵ and R⁷, independently of each other, represent an alkyl,aryl, aralkyl or alkylaryl group and R⁶ is a divalent alkyl, aryl,aralkyl or alkaryl group, p is 0, 1, 2, 3, inclusive, m and n are,independently, an integer from 2, 3, 4, 5, inclusive; x and y are,independently, integers from 1 to 350, inclusive and z is from 0 to 200,inclusive; adding a first portion of retarder to the slurry, the firstportion being an amount of retarder sufficient to substantially preventbuildup of gypsum crystals within the mixer; adding a second portion ofretarder to the slurry, the second portion being an amount of retardersufficient to increase the fluidity of the slurry beyond that obtainedby addition of the first portion of retarder.
 2. The method of claim 1further comprising selecting the retarder to synergistically increasefluidity in combination with the dispersant.
 3. The method of claim 1wherein said first adding step and said second adding step are combined.4. The method of claim 1 further comprising combining the defoamer andthe dispersant prior to said preparing step.
 5. The method of claim 4wherein said combining step comprises blending the dispersant and thedefoamer in an aqueous carrier.
 6. The method of claim 4 wherein saidcombining step comprises chemically or physically attaching the defoamerto the dispersant.
 7. The method of claim 6 wherein said combining stepincludes co-polymerizing a defoaming moiety with the olefinicunsaturated mono-carboxylic acid moiety and the (poly)oxyalkylenemoiety.
 8. The method of claim 1 wherein the retarder of the firstadding step comprises an acid or salt of diethylenetriaminepentaacetate.9. The method of claim 8 wherein the retarder comprises a sodium salt.10. The method of claim 9 wherein the retarder comprises a pentasodiumsalt.
 11. The method of claim 1 wherein the retarder of the secondadding step comprises an acid or sodium, potassium, ammonium or lithiumsalt of diethylenetriaminepentaacetate, penta sodium salt of aminotri(methylene phosphonic acid), tartaric acid, succinic acid, citricacid, maleic acid.
 12. The method of claim 11 wherein the retardercomprises a sodium salt.
 13. The method of claim 11 wherein the retardercomprises a pentasodium salt of diethylenetriaminepentaacetate.
 14. Agypsum slurry comprising: calcined gypsum; water; a first portion of aretarder, said first portion being an amount sufficient to substantiallyprevent formation of gypsum crystals within the mixer; a second portionof the retarder, said second portion being an amount of retardersufficient to increase the fluidity of the slurry beyond that obtainedby addition of the first portion of retarder; a defoamer; and adispersant, wherein said dispersant consists essentially of a first anda second repeating unit, wherein said first repeating unit is anolefinic unsaturated mono-carboxylic acid repeating unit or an ester orsalt thereof, or an olefinic unsaturated sulphuric acid repeating unitor a salt thereof, and said second repeating unit is of the generalformula (I)

where R¹ is represented by

and wherein R² is hydrogen or an aliphatic C₁ to C₅ hydrocarbon group,R³ is a non-substituted or substituted aryl group, and R⁴ is hydrogen oran aliphatic C₁ to C₂₀ hydrocarbon group, a cycloaliphatic C₅ to C₈hydrocarbon group, a substituted C₆ to C₁₄ aryl group or a groupconforming to the formula

wherein R⁵ and R⁷, independently of each other, represent an alkyl,aryl, aralkyl or alkylaryl group and R⁶ is a divalent alkyl, aryl,aralkyl or alkaryl group, p is 0, 1, 2, 3, inclusive, m and n are,independently, an integer from 2, 3, 4, 5, inclusive; x and y are,independently, integers from 1 to 350, inclusive and z is from 0 to 200,inclusive.
 15. The slurry of claim 14 wherein said first portion ofretarder is about 0.1 to about 1 lb/MSF.
 16. The slurry of claim 13wherein said second portion of retarder is about 0.05 to about 0.3lb/MSF.
 17. The slurry of claim 15 wherein said defoamer is combinedwith said dispersant prior to addition to said slurry.
 18. The slurry ofclaim 17 wherein said defoamer is blended with said dispersant in acarrier.
 19. The slurry of claim 17 wherein said defoamer is physicallyor chemically attached to said dispersant.
 20. The slurry of claim 19wherein said defoamer is a third moiety in said dispersant structure.21. The slurry of claim 15 wherein at least one of said first retarderand said second retarder is an acid or salt ofdiethylenetriaminepentaacetate.